grammar 問題

一句句子可以有2種 tense because there is no rules that it cannot. A sentence is made up of one or more clauses. The clauses in a sentence can be in different tenses.
There are two clauses in the sentence "There are portable electronic books,but no one seems to have bought them." Both clauses are in present tense.

前者用present tense 因為要表達一些恆久的, 慣常的, 自然的事實及現象!!!e.g太陽從東面昇起, 一定是用present tense

後者用present perfect tense因為要表達有些現象現在此刻, 預計會維持一段時間的, 就要用present perfect tense


希望幫到你啦